Widget in menu bar

Hi, I'm trying to get a custom search box into the main nav bar. This doesn't seem possible.

So then I put the search widget in the top bar (or header) and added the nav there. But then the buttons become basic links that I need to build up from.

Is there a way to simulate one contiguous black bar, with search widget on the left side, and main nav bar on the right?

I thought I saw bits of this in your overview video, shrinking the main nav to the right. Then I can make a black background, and shrink the height to be the same height as the main nav.